How to route To different MasterPages in sharepoint?

Question

I 'm trying to create a HttpModule that allows to route to different MasterPage preInt event. I' not an Expert about MasterPages. I'm trying to nderstand about MasterPages Token. I knows there are three type: custom and Default. In this tutorial I found this code :

void page_PreInit(object sender, EventArgs e)
    {
        Page page = sender as Page;
        string pageNo = ConfigurationManager.AppSettings["MasterPageNo"];




        if (page != null)
        {
            if (pageNo.Equals("1"))
            {
                page.MasterPageFile = "~masterurl/custom.master";
                if (SPContext.Current != null)
                {
                    SPContext.Current.Web.CustomMasterUrl = "/_catalogs/masterpage/custom1.master";
                }
            }
            else if (pageNo.Equals("2"))
            {
                page.MasterPageFile = "~masterurl/custom.master";
                if (SPContext.Current != null)
                {
                    SPContext.Current.Web.CustomMasterUrl = "/_catalogs/masterpage/custom2.master";
                }


            }
            else
            {
                page.MasterPageFile = "~masterurl/default.master";
                if (SPContext.Current != null)
                {
                    SPContext.Current.Web.MasterUrl = "/_catalogs/masterpage/default.master";
                }
            }


        } 

In Sharepoint , I have three MasterPages :

-Default.Master -GeneraliTeamSite.MasterPage.Master -GeneraliTeamSiteWiki.MasterPage.Master.master

With Sp Designer, I have set Default.master as Default, GeneraliTeamSite.MasterPage.Master as Custom. Now if i Run the page, I got this exception :

The file '/_layouts/~masterurl/custom.master' does not exist.   at System.Web.UI.Util.CheckVirtualFileExists(VirtualPath virtualPath) 
   at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile) 
   at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile) 
   at System.Web.Compilation.BuildManager.GetVPathBuildResult(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile) 
   at System.Web.UI.MasterPage.CreateMaster(TemplateControl owner, HttpContext context, VirtualPath masterPageFile, IDictionary contentTemplateCollection) 
   at System.Web.UI.Page.get_Master() 
   at System.Web.UI.Page.ApplyMasterPage() 
   at System.Web.UI.Page.PerformPreInit() 
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Answer 1

Basically, the code looks very good, although i noticed one error:

Here is how to set the new masterpage:

page.MasterPageFile="~/_catalogs/masterpage/v4_minimal.master"

Because what you did is:

page.MasterPageFile = "~masterurl/custom.master";

And this will not work due to a wrong path ...

Here is the full example, but check for the correct path ...

if (page.MasterPageFile != null)
{
    page.MasterPageFile = "~/_catalogs/masterpage/custom.master";
    if (pageNo.Equals("1"))
    {
        if (SPContext.Current != null)
        {
            SPContext.Current.Web.CustomMasterUrl = "/_catalogs/masterpage/custom1.master";
        }
    }
    else if (pageNo.Equals("2"))
    {
        if (SPContext.Current != null)
        {
            SPContext.Current.Web.CustomMasterUrl = "/_catalogs/masterpage/custom2.master";
        }
    }
    else
    {
        page.MasterPageFile = "~/_catalogs/masterpage/default.master";
        if (SPContext.Current != null)
        {
            SPContext.Current.Web.MasterUrl = "/_catalogs/masterpage/default.master";
        }
    }
}

Hope it was usefull!

Happy coding!

Answer 2

This is some code I've used in the past to dynamically set the masterpage based on a querystring in the URL.

protected override void OnPreInit(EventArgs e) {
    base.OnPreInit(e);
    if (this.Request.Url.AbsoluteUri.Contains("frame=true")) {
        this.MasterPageFile = "framed.master";
    }
}

http://mike-greene.com/2011/10/dynamic-master-page-logic/